When I was a kid-my parents never had us leave...
When DH and I started going together, we always took the mid-day break since we always stay on property (YC/BC)
Now that we have kids, it's a necessity... ESPECIALLY when we go in August!!!
We generally are there for the rope drop and leave after lunch... then return to a different park for dinner and the evening.
Last year we were asked to be a family of the day in AK and ride in the parade

That meant we couldn't leave the park since we had to be @ the parade entrance @ 3:30pm and AK is kind of a pain to get back to via Disney Transportation. It was 98 degrees and so humid you could cut the air with a knife. We did Kali River Rapids around 2:30 to try to cool down, but our side barely got wet

By the time we had to get on the float for the parade, we were drenched with sweat

Ewwwwwww Our girls were cranky as anything but held up ok for the waving/smiling from the float....

We had a blast doing that, but you'd better believe we high-tailed it out of the park after the parade by 4:30/5 and didn't do a park that night

Cancelled our ADR's and just ate at the hotel and swam in Stormalong Bay all evening....
So.... yes-we ALWAYS take a mid-day break

even just to shower/refresh/swim

esp. in August!